Slide projectors and trays, particularly those using circular trays, are well known in the art. (See, for example, U.S. Pat. No. 3,499,708 and U.S. Pat. No. 3,411,845). In particular, the series of projectors made by Kodak (.TM.) in their Carousel (.TM.) line use a gravity feed system having a horizontally disposed circular tray to project slides (see U.S. Pat. No. 3,276,314).
In many applications, however, it is important to align two projectors to cover the same image area so that a programmable lap dissolve may be used to fade from one slide to the next, or simulate motion by simple animation or rapid slide change. These functions must necessarily be performed by two projectors or otherwise a projector with two projection means and separately addressable slide trays. One such system is that shown in U.S. Pat. No. 3,718,392 which employs two straight-line slide trays interlocked into a side-by-side relationship. This limits the unit to sequential slide access to slides immediately preceding and following the projected slide. Unfortunately, straight-line slide trays have not been convenient for projecting a large series of slides as the length necessary for the tray becomes prohibitive. Furthermore, if the dissolve programming indicates the need to superimpose an image over three or four other images, the effect has to be simulated by the use of additional slides which would use up more of the limited tray space. In addition, if the slides are projected out of sequence involving random access, a straight-line slide tray will have inordinately long access time where the slides have addresses which would be at opposite ends of the tray.
In the present invention, functions which could be performed by two separate slide projectors are combined into a single unitary machine using a unique circular tray which can independently and randomly access any slide in either of its concentric slide holding rings. Combining this single unit projection system with a programmable lap dissolve creates an effective tool for communication which is as easy to use as a single projector. Set up time and reliability are enhanced while the size of the machine and slide trays are capable of being produced in a convenient size such that they may be easily transported.